That was Iblis, a noble genie appointed by Sulymon (who was a genie at the time) who eventually misused his power. The current Grand Sultan is not the original instigator of the rebellion who was cursed by the gods.

Notes on the BBEG: I will first admit to an error in the previous post. He seeks to achieve godhood by invading as many worlds as possible and retrieving the soul of Sulymon, a mortal prophet who is believed necessary in restoring a shard of his former power. The once-scenic and nice City of Brass ended up his dominion ever since, and he's been pissed off ever since at life in general. As to why the latter, he wanted to enslave mortals who the gods sought to appoint as masters of the universe. The City of Brass is ruled over by the Grand Sultan of the Efreet, who back in primordial times was a tyrant who among other things caused a civil war among the genie clans and rebelled against the gods. Back in the day I read it and found it very much my jam, but as of 2020 Frog God Games wanted to revamp it for 5th Edition and the OSR, along with expanding the adventures into a true level 1 to 20 epic Adventure Path. For those not in the know, City of Brass' earlier incarnation was a city-based planar metropolis made during the final years of the 3.5 era, with some accompanying adventures.

For apple download City of Brass